Photosensor

ABSTRACT

A photosensor including: a first electrode; a second electrode; a photoelectric conversion layer between the first electrode and the second electrode; a first charge blocking layer between the first electrode and the photoelectric conversion layer; a second charge blocking layer between the second electrode and the photoelectric conversion layer; a voltage supply circuit supplying a voltage to the second electrode such that an electric field directed from the second electrode toward the first electrode is generated in the photoelectric conversion layer; and a transistor. The first charge blocking layer suppresses movement of holes from the photoelectric conversion layer to the first electrode and movement of electrons from the first electrode to the photoelectric conversion layer, and the second charge blocking layer suppresses movement of electrons from the photoelectric conversion layer to the second electrode and movement of holes from the second electrode to the photoelectric conversion layer.

BACKGROUND

This application is a Continuation of U.S. patent application Ser. No.15/939,381, filed on Mar. 29, 2018, which is a Continuation ofPCT/JP2016/003348, filed on Jul. 15, 2016, which in turn claims thebenefit of Japanese Application No. 2015-222063, filed on Nov. 12, 2015,and Japanese Application No. 2015-222064, filed on Nov. 12, 2015, theentire disclosures of which Applications are incorporated by referenceherein.

TECHNICAL FIELD

The present disclosure relates to a photosensor.

DESCRIPTION OF THE RELATED ART

Photodetection elements have conventionally been used forphotodetectors, image sensors, etc. Typical examples of thephotodetection elements include photodiodes and phototransistors. As iswell known, when a photoelectric conversion element is irradiated withlight, a photocurrent is generated, and the light can be detected bydetecting the photocurrent.

Japanese Unexamined Patent Application Publication No. 2011-60830discloses in FIG. 2 a thin film transistor (TFT) including, as a gateinsulating film, an organic film in which a prescribed compound isdispersed in an organic polymer. A compound whose polarization statechanges when it is irradiated with light is selected as the compoundincluded in the organic film. In the thin film transistor in JapaneseUnexamined Patent Application Publication No. 2011-60830, when the gateinsulating film is irradiated with light, the permittivity of the gateinsulating film changes. Therefore, an electric current flowing betweenthe source and the drain changes when the gate insulating film isirradiated with light. It is stated in Japanese Unexamined PatentApplication Publication No. 2011-60830 that such a thin film transistorcan be used for a photosensor.

SUMMARY

One non-limiting and exemplary embodiment provides a photosensor havinga novel structure.

In one general aspect, the techniques disclosed here feature aphotosensor comprising: a first electrode; a second electrode; aphotoelectric conversion layer between the first electrode and thesecond electrode, the photoelectric conversion layer generating electriccharges by photoelectric conversion; a first charge blocking layerbetween the first electrode and the photoelectric conversion layer; asecond charge blocking layer between the second electrode and thephotoelectric conversion layer; a voltage supply circuit configured tosupply a voltage to the second electrode such that an electric fielddirected from the second electrode toward the first electrode isgenerated in the photoelectric conversion layer; and a transistor havinga gate connected to the first electrode. The first charge blocking layeris configured to suppress movement of holes from the photoelectricconversion layer to the first electrode and movement of electrons fromthe first electrode to the photoelectric conversion layer, and thesecond charge blocking layer is configured to suppress movement ofelectrons from the photoelectric conversion layer to the secondelectrode and movement of holes from the second electrode to thephotoelectric conversion layer.

It should be noted that general or specific embodiments may beimplemented as an element, a device, an apparatus, a system, a method,an integrated circuit, a computer program, a storage medium, or anyselective combination thereof.

Additional benefits and advantages of the disclosed embodiments willbecome apparent from the specification and drawings. The benefits and/oradvantages may be individually obtained by the various embodiments andfeatures of the specification and drawings, which need not all beprovided in order to obtain one or more of such benefits and/oradvantages.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram for illustrating a change in permittivityin response to irradiation with light;

FIG. 2 is a schematic diagram illustrating an exemplary structure of aphotosensor according to a first embodiment of the present disclosure;

FIG. 3 is an exemplary energy diagram of a photodetection element 10Ashown in FIG. 2;

FIG. 4 is an exemplary energy diagram of an imaging element having anorganic thin film and shown as a comparative example;

FIG. 5 is a graph showing an example of an absorption spectrum in aphotoelectric conversion layer formed from a material containing tinnaphthalocyanine;

FIG. 6 is a schematic cross-sectional view showing an example of thestructure of a photodetection element including a photoelectricconversion layer formed using an organic semiconductor materialcontaining tin naphthalocyanine represented by general formula (1);

FIG. 7 is an exemplary energy diagram of a photodetection element inwhich a hole blocking layer and a photoelectric conversion layer aredisposed between a first electrode and a second electrode;

FIG. 8 is an energy diagram showing an example of the relative relationsamong the energies of the components of the photodetection elementincluding the hole blocking layer disposed between the first electrodeand the photoelectric conversion layer;

FIG. 9 is an exemplary energy diagram of a photodetection element inwhich the photoelectric conversion layer and an electron blocking layerare disposed between the first electrode and the second electrode;

FIG. 10 is an energy diagram showing an example of the relativerelations among the energies of the components of the photodetectionelement including the electron blocking layer disposed between thephotoelectric conversion layer and the second electrode;

FIG. 11 is a schematic diagram showing an exemplary structure of aphotosensor according to a second embodiment of the present disclosure;

FIG. 12 is an exemplary energy diagram of a photodetection element shownin FIG. 11;

FIG. 13 is an exemplary energy diagram of a photodetection element inwhich an insulating layer and a photoelectric conversion layer aredisposed between a first electrode and a second electrode;

FIG. 14 is an energy diagram showing an example of the relativerelations among the energies of the components of the photodetectionelement including the insulating layer disposed between the firstelectrode and the photoelectric conversion layer;

FIG. 15 is an exemplary energy diagram of a photodetection element inwhich the photoelectric conversion layer and an insulating layer aredisposed between the first electrode and the second electrode;

FIG. 16 is an energy diagram showing an example of the relativerelations among the energies of the components of the photodetectionelement including the insulating layer disposed between thephotoelectric conversion layer and the second electrode;

FIG. 17 is a schematic diagram showing the structure of a photodetectionelement used to measure a change in permittivity;

FIG. 18 is a graph showing the results of measurement of the capacitancevalue of a dielectric structure of the photodetection element;

FIG. 19 is a schematic cross-sectional view showing an example of thedevice structure of a photodetection element;

FIG. 20 is a schematic cross-sectional view showing another example ofthe device structure of the photodetection element;

FIG. 21 is a schematic cross-sectional view showing yet another exampleof the device structure of the photodetection element;

FIG. 22 is a schematic cross-sectional view showing still anotherexample of the device structure of the photodetection element; and

FIG. 23 is a graph showing the film thickness dependence of a leakagecurrent flowing through a silicon oxide film when a voltage of 2.5 V isapplied.

DETAILED DESCRIPTION

Aspects of the present disclosure are summarized as follows.

Item 1

A photosensor comprising:a first electrode and a second electrode, at least one of the firstelectrode and the second electrode having light-transmitting properties;a photoelectric conversion layer disposed between the first electrodeand the second electrode;a voltage supply circuit that supplies a first voltage and a secondvoltage higher than the first voltage to the first electrode and thesecond electrode, respectively; anda hole blocking layer disposed between the first electrode and thephotoelectric conversion layer, whereinthe photosensor outputs an electric signal that corresponds to a changein permittivity between the first electrode and the second electrode,the change in permittivity being caused by incident light to thephotoelectric conversion layer through at least one of the firstelectrode and the second electrode.

In the structure in item 1, movement of electric charges generated byphotoelectric conversion to the electrodes is suppressed, and theelectric charges generated by photoelectric conversion can be utilizedas electric charges contributing to the change in permittivity betweenthe two electrodes.

Item 2

The photosensor according to item 1, further comprising:a semiconductor layer disposed between the hole blocking layer and thefirst electrode; anda third electrode disposed in contact with the semiconductor layer,whereinthe first electrode is disposed in contact with the semiconductor layerso as to be spaced apart from the third electrode, andthe electric signal is outputted from the third electrode.

In the structure in item 2, the change in permittivity in the dielectricstructure between the first electrode and the second electrode can bedetected as a change in electric current flowing between the firstelectrode and the third electrode.

Item 3

The photosensor according to item 1 or 2, wherein the ionizationpotential of the photoelectric conversion layer is higher than the workfunction of the second electrode.

In the structure in item 3, a potential barrier can be formed betweenthe second electrode and the photoelectric conversion layer. Thepotential barrier between the second electrode and the photoelectricconversion layer can suppress movement of holes from the secondelectrode to the photoelectric conversion layer.

Item 4

The photosensor according to item 1 or 2, further comprisingan electron blocking layer disposed between the second electrode and thephotoelectric conversion layer.

In the structure in item 4, the electron blocking layer can effectivelysuppress movement of electrons from the photoelectric conversion layerto the second electrode.

Item 5

A photosensor comprising:a first electrode and a second electrode, at least one of the firstelectrode and the second electrode having light-transmitting properties;a photoelectric conversion layer disposed between the first electrodeand the second electrode;a voltage supply circuit that supplies a first voltage and a secondvoltage higher than the first voltage to the first electrode and thesecond electrode, respectively; andan electron blocking layer disposed between the second electrode and thephotoelectric conversion layer, whereinthe photosensor outputs an electric signal that corresponds to a changein permittivity between the first electrode and the second electrode,the change in permittivity being caused by incident light to thephotoelectric conversion layer through at least one of the firstelectrode and the second electrode.

In the structure in item 5, movement of electric charges generated byphotoelectric conversion to the electrodes is suppressed, and theelectric charges generated by photoelectric conversion can be utilizedas electric charges contributing to the change in permittivity betweenthe two electrodes.

Item 6

The photosensor according to item 5, further comprising:a semiconductor layer disposed between the electron blocking layer andthe second electrode; anda third electrode disposed in contact with the semiconductor layer,whereinthe second electrode is disposed in contact with the semiconductor layerso as to be spaced apart from the third electrode, andthe electric signal is outputted from the third electrode.

In the structure in item 6, the change in permittivity in the dielectricstructure between the first electrode and the second electrode can bedetected as a change in electric current flowing between the secondelectrode and the third electrode.

Item 7

The photosensor according to item 5 or 6, wherein the electron affinityof the photoelectric conversion layer is lower than the work function ofthe first electrode.

In the structure in item 7, a potential barrier can be formed betweenthe first electrode and the photoelectric conversion layer. Thepotential barrier between the first electrode and the photoelectricconversion layer can suppress movement of electrons from the firstelectrode to the photoelectric conversion layer.

Item 8

The photosensor according to item 5 or 6, further comprisinga hole blocking layer disposed between the first electrode and thephotoelectric conversion layer.

In the structure in item 8, the hole blocking layer can effectivelysuppress movement of holes from the photoelectric conversion layer tothe first electrode.

Item 9

A photosensor comprising:a first electrode and a second electrode, at least one of the firstelectrode and the second electrode having light-transmitting properties;a photoelectric conversion layer disposed between the first electrodeand the second electrode;a voltage supply circuit that supplies a first voltage and a secondvoltage higher than the first voltage to the first electrode and thesecond electrode, respectively; andan insulating layer disposed between the first electrode and thephotoelectric conversion layer, whereinthe photosensor outputs an electric signal that corresponds to a changein permittivity between the first electrode and the second electrode,the change in permittivity being caused by incident light to thephotoelectric conversion layer through at least one of the firstelectrode and the second electrode.

In the structure in item 9, movement of electric charges generated byphotoelectric conversion to the electrodes is suppressed, and theelectric charges generated by photoelectric conversion can be utilizedas electric charges contributing to the change in permittivity betweenthe two electrodes.

Item 10

The photosensor according to item 9, further comprising:a semiconductor layer disposed between the insulating layer and thefirst electrode; anda third electrode disposed in contact with the semiconductor layer,whereinthe first electrode is disposed in contact with the semiconductor layerso as to be spaced apart from the third electrode, andthe electric signal is outputted from the third electrode.

In the structure in item 10, the change in permittivity in thedielectric structure between the first electrode and the secondelectrode can be detected as a change in electric current flowingbetween the first electrode and the third electrode.

Item 11

The photosensor according to item 9 or 10, whereinthe ionization potential of the photoelectric conversion layer is higherthan the work function of the second electrode.

In the structure in item 11, a potential barrier can be formed betweenthe second electrode and the photoelectric conversion layer. Thepotential barrier between the second electrode and the photoelectricconversion layer can suppress movement of electrons from the secondelectrode to the photoelectric conversion layer.

Item 12

The photosensor according to item 9 or 10, further comprisinga second insulating layer disposed between the second electrode and thephotoelectric conversion layer.

In the structure in item 12, the second insulating layer disposedbetween the second electrode and the photoelectric conversion layer canmore reliably suppress the movement of the electric charges between thesecond electrode and the photoelectric conversion layer.

Item 13

A photosensor comprising:a first electrode and a second electrode, at least one of the firstelectrode and the second electrode having light-transmitting properties;a photoelectric conversion layer disposed between the first electrodeand the second electrode;a voltage supply circuit that supplies a first voltage and a secondvoltage higher than the first voltage to the first electrode and thesecond electrode, respectively; andan insulating layer disposed between the second electrode and thephotoelectric conversion layer, whereinthe photosensor outputs an electric signal that corresponds to a changein permittivity between the first electrode and the second electrode,the change in permittivity being caused by incident light to thephotoelectric conversion layer through at least one of the firstelectrode and the second electrode.

In the structure in item 13, movement of electric charges generated byphotoelectric conversion to the electrodes is suppressed, and theelectric charges generated by photoelectric conversion can be utilizedas electric charges contributing to the change in permittivity betweenthe two electrodes.

Item 14

The photosensor according to item 13, further comprising:a semiconductor layer disposed between the insulating layer and thesecond electrode; anda third electrode disposed in contact with the semiconductor layer,whereinthe second electrode is disposed in contact with the semiconductor layerso as to be spaced apart from the third electrode, andthe electric signal is outputted from the third electrode.

In the structure in item 14, the change in permittivity in thedielectric structure between the first electrode and the secondelectrode can be detected as a change in electric current flowingbetween the second electrode and the third electrode.

Item 15

The photosensor according to item 13 or 14, wherein the electronaffinity of the photoelectric conversion layer is higher than the workfunction of the first electrode.

In the structure in item 15, a potential barrier can be formed betweenthe first electrode and the photoelectric conversion layer. Thepotential barrier between the first electrode and the photoelectricconversion layer can suppress movement of electrons from the firstelectrode to the photoelectric conversion layer.

Item 16

The photosensor according to item 13 or 14, further comprisinga second insulating layer disposed between the first electrode and thephotoelectric conversion layer.

In the structure in item 16, the second insulating layer disposedbetween the first electrode and the photoelectric conversion layer canmore reliably suppress the movement of electric charges between thefirst electrode and the photoelectric conversion layer.

Item 17

A photosensor comprising:a first electrode;a second electrode facing the first electrode;a photoelectric conversion layer located between the first electrode andthe second electrode, the photoelectric conversion layer generatingelectric charges by photoelectric conversion;a first charge blocking layer located between the first electrode andthe photoelectric conversion layer;a second charge blocking layer located between the second electrode andthe photoelectric conversion layer;a voltage supply circuit connected to at least one of the firstelectrode and the second electrode, the voltage supply circuit applyinga voltage to the at least one of the first electrode and the secondelectrode such that an electric field directed from the second electrodetoward the first electrode is generated in the photoelectric conversionlayer; anda detection circuit that detects a signal corresponding to a change incapacitance between the first electrode and the second electrode, thechange in capacitance being caused by incident light to thephotoelectric conversion layer, whereinthe first charge blocking layer suppresses movement of holes from thephotoelectric conversion layer to the first electrode and movement ofelectrons from the first electrode to the photoelectric conversionlayer, andthe second charge blocking layer suppresses movement of electrons fromthe photoelectric conversion layer to the second electrode and movementof holes from the second electrode to the photoelectric conversionlayer.

Item 18

The photosensor according to item 17, whereinthe voltage supply circuit applies a voltage to one of the firstelectrode and the second electrode, andthe detection circuit detects a voltage of the other one of the firstelectrode and the second electrode.

Item 19

The photosensor according to item 18, further comprisinga capacitor having a first end connected to the other one of the firstelectrode and the second electrode and a second end to which aprescribed voltage is applied.

Item 20

The photosensor according to item 17, further comprising:a semiconductor layer located between the second charge blocking layerand the second electrode, the semiconductor layer being in contact withthe second electrode; anda third electrode in contact with the semiconductor layer, whereinthe voltage supply circuit applies a voltage to the first electrode andthe second electrode, andthe detection circuit detects an electric current flowing between thesecond electrode and the third electrode.

Item 21

The photosensor according to item 17, further comprising:a semiconductor layer located between the first charge blocking layerand the first electrode, the semiconductor layer being in contact withthe first electrode; anda third electrode in contact with the semiconductor layer, whereinthe voltage supply circuit applies a voltage to the first electrode andthe second electrode, andthe detection circuit detects an electric current flowing between thefirst electrode and the third electrode.

Item 22

The photosensor according to item 17, whereinthe voltage supply circuit applies, between the first electrode and thesecond electrode, a voltage obtained by superimposing a first voltage ona second voltage, the first voltage having an amplitude that variesperiodically, the second voltage being a DC voltage that causes anelectric field directed from the second electrode toward the firstelectrode to be generated in the photoelectric conversion layer, andthe detection circuit detects an electric current flowing between thefirst electrode and the second electrode.

Item 23

The photosensor according to item 17, further comprisinga current supply circuit that applies, between the first electrode andthe second electrode, an electric current having an amplitude thatvaries periodically, whereinthe voltage supply circuit applies a DC voltage between the firstelectrode and the second electrode such that an electric field directedfrom the second electrode toward the first electrode is generated in thephotoelectric conversion layer, andthe detection circuit detects a potential difference between the firstelectrode and the second electrode.

Item 24

The photosensor according to any one of items 17 to 23, whereinthe HOMO level of the first charge blocking layer is deeper than theHOMO level of the photoelectric conversion layer by at least 0.3 eV, andthe LUMO level of the first charge blocking layer is shallower than theFermi level of the first electrode by at least 0.3 eV.

Item 25

The photosensor according to any one of items 17 to 24, whereinthe LUMO level of the second charge blocking layer is shallower than theLUMO level of the photoelectric conversion layer by at least 0.3 eV, andthe HOMO level of the second charge blocking layer is deeper than theFermi level of the second electrode by at least 0.3 eV.

Item 26

The photosensor according to any one of items 17 to 25, wherein at leastone of the first charge blocking layer and the second charge blockinglayer is an insulating layer.

Item 27

A photosensor comprising:a first electrode;a second electrode facing the first electrode;a photoelectric conversion layer located between the first electrode andthe second electrode, the photoelectric conversion layer generatingelectric charges by photoelectric conversion;a first insulating layer located between the first electrode and thephotoelectric conversion layer;a second insulating layer located between the second electrode and thephotoelectric conversion layer;a voltage supply circuit connected to at least one of the firstelectrode and the second electrode, the voltage supply circuit applyinga voltage to the at least one of the first electrode and the secondelectrode such that an electric field is generated in the photoelectricconversion layer; anda detection circuit that detects a signal corresponding to a change incapacitance between the first electrode and the second electrode, thechange in capacitance being caused by incident light to thephotoelectric conversion layer.

Item 28

The photosensor according to item 27, whereinthe voltage supply circuit applies a voltage to one of the firstelectrode and the second electrode, andthe detection circuit detects a voltage at the other one of the firstelectrode and the second electrode.

Item 29

The photosensor according to item 28, further comprisinga capacitor having a first end connected to the other one of the firstelectrode and the second electrode and a second end to which aprescribed voltage is applied.

Item 30

The photosensor according to item 27, further comprising:a semiconductor layer located between the second insulating layer andthe second electrode, the semiconductor layer being in contact with thesecond electrode; anda third electrode in contact with the semiconductor layer, whereinthe voltage supply circuit applies a voltage to the first electrode andthe second electrode, andthe detection circuit detects an electric current flowing between thesecond electrode and the third electrode.

Item 31

The photosensor according to item 27, whereinthe voltage supply circuit applies, between the first electrode and thesecond electrode, voltage obtained by superimposing a first voltage on asecond voltage, the first voltage having an amplitude that variesperiodically, the second voltage being a DC voltage that causes anelectric field directed from the second electrode toward the firstelectrode to be generated in the photoelectric conversion layer, andthe detection circuit detects an electric current flowing between thefirst electrode and the second electrode.

Item 32

The photosensor according to item 27, further comprisinga current supply circuit that applies, between the first electrode andthe second electrode, an electric current having an amplitude thatvaries periodically, whereinthe voltage supply circuit applies a DC voltage between the firstelectrode and the second electrode such that an electric field directedfrom the second electrode toward the first electrode is generated in thephotoelectric conversion layer, andthe detection circuit detects a potential difference between the firstelectrode and the second electrode.

Embodiments of the present disclosure will next be described in detailwith reference to the drawings. The embodiments described below showgeneral or specific examples. Numerical values, shapes, materials,components, arrangements and connections of the components, steps, theorder of the steps, etc. shown in the following embodiments are examplesand are not intended to limit the present disclosure. Various aspectsdescribed herein can be mutually combined so long as no conflict arises.Among the components in the following embodiments, components notdescribed in independent claims representing the broadest concepts aredescribed as optional components. In the following description,components having substantially the same functions are denoted by thesame reference numerals, and their description may be omitted.

Principle of Photodetection

Before the embodiments of the present disclosure are described indetail, an outline of the principle of photodetection will first bedescribed. As will be described later in detail with reference to thedrawings, a photosensor according to an embodiment of the presentdisclosure includes a photodetection element having a general structurein which a dielectric structure is sandwiched between two electrodes.The dielectric structure disposed between the two electrodes typicallyincludes a photoelectric conversion layer that generates electriccharges when irradiated with light. In the embodiments described below,light is detected by using a change in the permittivity of thedielectric structure due to the light entering the photoelectricconversion layer.

FIG. 1 is an illustration for describing the outline of the principle ofphotodetection in an embodiment of the present disclosure. FIG. 1schematically shows an element 90 including two electrodes 91 and 92 anda dielectric structure 94 sandwiched between them. FIG. 1 schematicallyshows the state in which a DC power source is connected to theelectrodes 91 and 92 and an electric field is thereby applied from theoutside to the dielectric structure 94.

When the electric field is formed between the electrode 91 and theelectrode 92, polarization occurs in the dielectric structure 94. Anarrow P in FIG. 1 represents dielectric polarization in the dielectricstructure 94. An arrow D represents electric flux density. σ_(f) is thedensity of electric charges in the electrodes, and σ_(p) is the densityof electric charges generated by polarization within the dielectricstructure 94 at its surfaces facing the electrodes.

Let the magnitude of the electric field in the dielectric structure 94be E. According to the Gauss' law, E=((σ_(f)−σ_(p))/ε₀) and E=(σ_(f)/ε)hold. ε₀ and ε are the permittivity of vacuum and the permittivity ofthe dielectric structure 94, respectively. From E=((σ_(f)−σ_(p))/ε₀) andE=(σ_(f)/ε), ε=ε₀ (σ_(f)/(σ_(f)−σ_(p))) is obtained. As can be seen fromthis formula, as the charge density σ_(p) increases, the permittivity ofthe dielectric structure 94 increases.

In this embodiment of the present disclosure, the dielectric structure94 used is a structure including a photoelectric conversion layer.Therefore, when light enters the dielectric structure 94, hole-electronpairs are generated in the photoelectric conversion layer. In thisexample, since a prescribed voltage is supplied between the electrodes91 and 92 disposed so as to face each other with the dielectricstructure 94 interposed therebetween, an electric field directed fromthe electrode 91 toward the electrode 92 is formed in the photoelectricconversion layer in the dielectric structure 94. This causes the holesand electrons formed in the photoelectric conversion layer byphotoelectric conversion to be separated from each other. Part of theholes move toward the electrode 92, and part of the electrons movetoward the electrode 91.

Suppose that the electric charges generated by photoelectric conversionare not extracted from the dielectric structure 94 to the outsidethrough the electrode 91 or the electrode 92. In other words, the holesand electrons generated by photoelectric conversion are separated fromeach other, and the separated state is maintained. In this case, theseparated charges cause the charge density σ_(p) to increaseeffectively. When the charge density σ_(p) increases, the permittivityof the dielectric structure 94 increases, as described above. This meansthat, when light enters the dielectric structure 94, the permittivitybetween the electrodes 91 and 92 changes. Specifically, by separatingthe holes and electrons generated by photoelectric conversion from eachother while the separated charges are retained in the dielectricstructure, the capacitance value between the electrode 91 and theelectrode 92 is changed. By detecting the change in the capacitancevalue, the light entering the dielectric structure 94 can be detected.

Photosensors in the embodiments described below each have a structurecapable of detecting light on the basis of a change in permittivitybetween two electrodes. It should be noted that, in the embodiments ofthe present disclosure, no electric charges are exchanged between thephotoelectric conversion layer and the electrodes. Specifically, theelectric charges generated in the photoelectric conversion layer byirradiation with light are retained within the photoelectric conversionlayer and are basically not transferred to the electrodes. Basically, noelectric charges are supplied from the electrodes to the photoelectricconversion layer. This is one of the differences from conventional solarcells and light emitting diodes utilizing photoelectric conversion.

First Embodiment of Photosensor

FIG. 2 shows the outline of an exemplary structure of a photosensoraccording to a first embodiment of the present disclosure. Thephotosensor 100A shown in FIG. 2 includes a photodetection element 10Aand a voltage supply circuit 12 connected to the photodetection element10A. The photodetection element 10A includes a first electrode 21, asecond electrode 22, and a dielectric structure 2A disposed therebetweenand including a photoelectric conversion layer 23A. FIG. 2 shows onlyschematically the arrangement of the components forming thephotodetection element 10A, and the dimensions of the components shownin FIG. 2 do not strictly reflect the dimensions of an actual device.The same also applies to other figures in the present disclosure.

Typically, a semiconductor material is used as the material forming thephotoelectric conversion layer 23A. In the photoelectric conversionlayer 23A, electron-hole pairs are generated in response to irradiationwith light. In this case, an organic semiconductor material is used asthe material forming the photoelectric conversion layer 23A. The detailsof the photoelectric conversion layer 23A will be described later.

The voltage supply circuit 12 is configured such that prescribedvoltages can be applied to the first electrode 21 and the secondelectrode 22. During photodetection, the voltage supply circuit 12supplies a first voltage to the first electrode 21 and supplies a secondvoltage higher than the first voltage to the second electrode 22. Thevoltage supply circuit 12 is not limited to a specific power sourcecircuit but may be a circuit generating the prescribed voltages or maybe a circuit that converts a voltage supplied from another power sourceto the prescribed voltages. The first voltage and/or the second voltagemay be applied in the form of pulses, or the application of the firstvoltage and/or the second voltage may be repeated periodically orquasi-periodically.

At least one of the first electrode 21 and the second electrode 22 is atransparent electrode. For example, when the second electrode 22 is atransparent electrode, the photoelectric conversion layer 23A receiveslight passing through the second electrode 22. Of course, the firstelectrode 21 to which the lower voltage is applied during photodetectionmay be a transparent electrode, or both the first electrode 21 and thesecond electrode 22 may be transparent electrodes.

The term “transparent” as used herein means that at least part of lightin a detection wavelength range is allowed to pass through, and it isnot necessary that light in the entire visible wavelength range beallowed to pass through. The light detected by the photosensor of thepresent disclosure is not limited to light in the visible wavelengthrange (e.g., of from 380 nm to 780 nm inclusive). Herein, generalelectromagnetic waves including infrared rays and ultraviolet rays areexpressed as “light” for convenience.

In the structure exemplified in FIG. 2, the dielectric structure 2Aincludes a hole blocking layer 20 h disposed between the first electrode21 and the photoelectric conversion layer 23A. The dielectric structure2A further includes an electron blocking layer 20 e disposed between thesecond electrode 22 and the photoelectric conversion layer 23A. The holeblocking layer 20 h and the electron blocking layer 20 e have thefunction of retaining, within the photoelectric conversion layer 23A,electric charges generated in the photoelectric conversion layer 23A byphotoelectric conversion. Specifically, the hole blocking layer 20 h hasthe function of suppressing movement of the holes generated byphotoelectric conversion to the first electrode 21. The electronblocking layer 20 e has the function of suppressing movement of theelectrons generated by photoelectric conversion to the second electrode22.

FIG. 3 is an exemplary energy diagram of the photodetection element 10A.In FIG. 3, a thick horizontal line on the left of three rectanglesrepresents the Fermi level of the first electrode 21, and a thickhorizontal line on the right of the three rectangles represents theFermi level of the second electrode 22. In FIG. 3, the base of theleftmost one of the three rectangles represents the energy level of thehighest occupied molecular orbital (HOMO) of the hole blocking layer 20h, and its side opposed to the base represents the energy level of thelowest unoccupied molecular orbital (LUMO). Similarly, the central andright rectangles in FIG. 3 schematically represent the HOMO and LUMOenergy levels of the photoelectric conversion layer 23A and the electronblocking layer 20 e, respectively. The same applies to other energydiagrams, unless otherwise specified.

During the photodetection operation, the first voltage is supplied fromthe voltage supply circuit 12 (not shown in FIG. 3, see FIG. 2) to thefirst electrode 21, and the second voltage higher than the first voltageis applied to the second electrode 22. Specifically, an electric fielddirected from the right to the left in FIG. 3 is applied to thephotoelectric conversion layer 23A from the outside. Thin arrows in theenergy diagram shown in FIG. 3 schematically indicate the directions ofthe voltages applied to the first electrode 21 and the second electrode22.

When light enters the photoelectric conversion layer 23A with the firstvoltage and the second voltage applied to the first electrode 21 and thesecond electrode 22, respectively, at least part of electric chargesgenerated by photoelectric conversion move along the electric fieldgenerated by the application of the first voltage and the secondvoltage. For example, the electrons generated move within thephotoelectric conversion layer 23A toward the second electrode 22.

However, since the electron blocking layer 20 e is disposed between thephotoelectric conversion layer 23A and the second electrode 22, movementof electrons from the photoelectric conversion layer 23A to the secondelectrode 22 is blocked by an energy barrier between the photoelectricconversion layer 23A and the electron blocking layer 20 e. Similarly,movement of holes from the photoelectric conversion layer 23A to thefirst electrode 21 is blocked by an energy barrier between thephotoelectric conversion layer 23A and the hole blocking layer 20 h.Specifically, movement of the electric charges generated byphotoelectric conversion to the electrodes is suppressed, and theelectric charges generated are retained within the photoelectricconversion layer 23A. As described above, in this embodiment of thepresent disclosure, the movement of the electric charges generated byphotoelectric conversion to the electrodes is suppressed.

In the example shown in FIG. 3, the difference between the HOMO energylevel of the photoelectric conversion layer 23A and the HOMO energylevel of the hole blocking layer 20 h is relatively large. Therefore, arelatively large potential barrier for holes is formed between thephotoelectric conversion layer 23A and the hole blocking layer 20 h. Inthis case, almost no holes move from the photoelectric conversion layer23A to the hole blocking layer 20 h. The HOMO energy level of the holeblocking layer 20 h is deeper by desirably at least 0.3 eV and moredesirably at least 0.7 eV than the HOMO energy level of thephotoelectric conversion layer 23A. Similarly, in the example shown inFIG. 3, the difference between the LUMO energy level of the electronblocking layer 20 e and the LUMO energy level of the photoelectricconversion layer 23A is relatively large, and therefore a relativelylarge potential barrier for electrons is formed between the electronblocking layer 20 e and the photoelectric conversion layer 23A. In thiscase, almost no electrons move from the photoelectric conversion layer23A to the electron blocking layer 20 e. The LUMO energy level of theelectron blocking layer 20 e is shallower than the LUMO energy level ofthe photoelectric conversion layer 23A by desirably at least 0.3 eV andmore desirably at least 0.7 eV.

In the above description, the hole blocking layer, the electron blockinglayer, and the photoelectric conversion layer are formed of organicmaterials. However, when these layers are formed of inorganic compounds,their HOMO is replaced with a valence band, and their LUMO is replacedwith a conduction band.

In the example shown in FIG. 3, the difference between the Fermi levelof the first electrode 21 and the LUMO energy level of the hole blockinglayer 20 h is relatively large. Therefore, a relatively high potentialbarrier for electrons is formed between the first electrode 21 and thehole blocking layer 20 h. In this case, almost no electrons are injectedfrom the first electrode 21 into the hole blocking layer 20 h. The LUMOenergy level of the hole blocking layer 20 h is shallower than the Fermilevel of the first electrode 21 by desirably at least 0.3 eV and moredesirably at least 0.7 eV. Similarly, in the example shown in FIG. 3,the difference between the HOMO energy level of the electron blockinglayer 20 e and the Fermi level of the second electrode 22 is relativelylarge. Therefore, a relatively high potential barrier for holes isformed between the electron blocking layer 20 e and the second electrode22. In this case, almost no holes are injected from the second electrode22 into the electron blocking layer 20 e. The HOMO energy level of theelectron blocking layer 20 e is deeper than the Fermi level of thesecond electrode 22 by desirably at least 0.3 eV and more desirably atleast 0.7 eV.

In the above description, the hole blocking layer, the electron blockinglayer, and the photoelectric conversion layer are formed of organicmaterials. When these layers are formed of inorganic materials, theirHOMO is replaced with a valence band, and their LUMO is replaced with aconduction band.

In this embodiment of the present disclosure, movement of electriccharges between the photoelectric conversion layer 23A and the firstelectrode 21 and movement of electric charges between the photoelectricconversion layer 23A and the second electrode 22 are suppressed. Forexample, the current density between the first electrode 21 and thesecond electrode 22 one second after the application of the voltagebetween the first electrode 21 and the second electrode 22 can be 1×10⁻⁹A/cm² or less. As described above, in this embodiment of the presentdisclosure, the electric charges generated by photoelectric conversioncan be utilized as electric charges contributing to the change in thepermittivity between the two electrodes (the first electrode 21 and thesecond electrode 22 in this case).

The photodetection element 10A exemplified above includes thephotoelectric conversion layer 23A formed using an organic semiconductormaterial. Known examples of a device utilizing photoelectric conversionby an organic thin film include an imaging element having an organicthin film and an organic thin film solar cell. Functional layers such asthe hole blocking layer and electron blocking layer may be used in theabove devices. However, the conventional structures differ from thestructure in this embodiment of the present disclosure in that theconventional structures must be configured such that electric chargesgenerated by photoelectric conversion can be extracted from thephotoelectric conversion layer to the electrodes along an electricfield.

FIG. 4 is an exemplary energy diagram of an imaging element having anorganic thin film and shown as a comparative example. In the structureshown in FIG. 4, a hole blocking layer 80 h is disposed between a pixelelectrode 82 and a photoelectric conversion layer 83, and an electronblocking layer 80 e is disposed between the photoelectric conversionlayer 83 and a transparent electrode 81 (e.g., an ITO electrode)disposed so as to face the pixel electrode 82.

Generally, in the imaging element using the organic thin film, aprescribed voltage is applied to the transparent electrode 81, and holesor electrons generated in the photoelectric conversion layer 83 arethereby collected as signal charges by the pixel electrode 82. Forexample, when a negative voltage is applied to the transparent electrode81, the pixel electrode 82 collects, as signal charges, electronsgenerated in the photoelectric conversion layer 83 by photoelectricconversion. For example, Al, TiN, Cu, Al, TaN, or ITO is used as thematerial of the pixel electrode 82.

It should be noted that, in the conventional imaging element using theorganic thin film, unlike in the photodetection element 10A describedabove, no hole blocking layer 80 h is disposed between the photoelectricconversion layer 83 and the electrode to which a lower voltage isapplied (the transparent electrode 81 in this case). Similarly, in theconventional imaging element using the organic thin film, no electronblocking layer 80 e is disposed between the photoelectric conversionlayer 83 and the electrode to which a higher voltage is applied (thepixel electrode 82 in this case).

As schematically shown in FIG. 4, in the imaging element in thecomparative example, the hole blocking layer 80 h is disposed betweenthe photoelectric conversion layer 83 and the electrode whose potentialis higher during operation (the pixel electrode 82 in this case). Theelectron blocking layer 80 e is disposed between the photoelectricconversion layer 83 and the electrode whose potential is lower duringoperation (the transparent electrode 81 in this case). Specifically, inthe conventional imaging element using the organic thin film, thearrangement of the hole blocking layer and the electron blocking layerrelative to the photoelectric conversion layer is inverted from that inthe photosensor according to this embodiment of the present disclosure.This is because, in the conventional imaging element using the organicthin film, the hole blocking layer 80 h is provided for the purpose ofallowing the electrons generated by photoelectric conversion toselectively pass therethrough from the photoelectric conversion layer 83to the pixel electrode 82 while injection of holes from the pixelelectrode 82 is suppressed. This is also because, in the conventionalimaging element using the organic thin film, the electron blocking layer80 e is provided for the purpose of allowing the holes generated byphotoelectric conversion to selectively pass therethrough from thephotoelectric conversion layer 83 to the transparent electrode 81 whileinjection of electrons from the transparent electrode 81 is suppressed.Also in a solar cell using an organic thin film, its hole blocking layermust have the function of allowing electrons to selectively pass throughwhile holes are blocked, and its electron blocking layer must have thefunction of allowing holes to selectively pass through while electronsare blocked.

The rate of discharge of electric charges from the photoelectricconversion layer 83 and the rate of inflow of electric charges into thephotoelectric conversion layer 83 are low. As described above, in thisembodiment of the present disclosure, no electric charges are exchangedbetween the photoelectric conversion layer 23A and the first electrode21 and between the photoelectric conversion layer 23A and the secondelectrode 22. In this embodiment of the present disclosure, it is onlynecessary that the positive and negative charges generated byphotoelectric conversion be separated from each other, and detection canbe performed at relatively high speed. Therefore, this embodiment of thepresent disclosure is advantageously applied to an image sensor. In thephotosensor according to this embodiment of the present disclosure, theholes or electrons generated by photoelectric conversion are notextracted as signal charges, and the amount of the signal charges is notread, so that a so-called reset operation is unnecessary. In thephotosensor according to this embodiment of the present disclosure, whenthe application of the electric field to the photoelectric conversionlayer is stopped, the holes and the electrons are recombined, and thepermittivity of the dielectric structure that has been increased byirradiation with light decreases. Specifically, in this embodiment ofthe present disclosure, a reset operation performed by supplying a resetvoltage is unnecessary, and this is advantageous to increase the speedof operation. It is unnecessary to provide a separate reset circuit, andthis is advantageous for miniaturization.

In this embodiment of the present disclosure, the configuration of thehole blocking layer 20 h and the electron blocking layer 20 e in thephotodetection element (e.g., the photodetection element 10A) isdetermined such that movement of electric charges from the photoelectricconversion layer 23A to the first electrode 21 and movement of electriccharges from the photoelectric conversion layer 23A to the secondelectrode 22 can be suppressed. For example, the materials of the firstelectrode 21, the hole blocking layer 20 h, the photoelectric conversionlayer 23A, the electron blocking layer 20 e, and the second electrode 22and the values of the first and second voltages are selected such thatthe relative relations among the energy levels of the components of thephotodetection element 10A and the direction of the voltage appliedbetween the first electrode 21 and the second electrode 22 are as shownin FIG. 3.

As described above, in the photosensor 100A, the movement of electriccharges from the photoelectric conversion layer 23A to the firstelectrode 21 and the movement of electric charges from the photoelectricconversion layer 23A to the second electrode 22 are suppressed.Therefore, the electric charges generated when light enters thephotoelectric conversion layer 23A through the first electrode 21 and/orthe second electrode 22 are retained within the photoelectric conversionlayer 23A. Since the electric charges generated by photoelectricconversion are retained within the photoelectric conversion layer 23A,the permittivity of the dielectric structure 2A including thephotoelectric conversion layer 23A increases. Specifically, thecapacitance value between the first electrode 21 and the secondelectrode 22 in the photosensor 100A changes when light enters thephotosensor 100A. By detecting the change in the capacitance valuebetween the first electrode 21 and the second electrode 22 as a changein electric current or voltage using an appropriate detection circuit,the light entering the photosensor 100A can be detected. As describedabove, the photosensor 100A can generate a signal corresponding to thechange in the permittivity of the dielectric structure 2A caused by theincident light.

The first voltage and/or second voltage is not necessarily a steadyconstant voltage and may be a voltage varying with time. In thisembodiment of the present disclosure, the second voltage used is higherthan the first voltage. However, this is not intended to completelyexclude the presence of the state in which the second voltage is equalto the first voltage. The second voltage is not limited to a voltagethat is always higher than the first voltage. When the voltages varywith time, the second voltage may be equal to the first voltage in someinstances.

One of the hole blocking layer 20 h and the electron blocking layer 20 ecan be omitted by selecting an appropriate combination of the materialsof the first electrode 21, the photoelectric conversion layer 23A, andthe second electrode 22 in consideration of the magnitude of theionization potential or electron affinity of the photoelectricconversion layer 23A and the magnitudes of the work functions of theelectrodes (the first electrode 21 and the second electrode 22).Examples of such a structure will be described later. The work functionof an electrode is defined as the difference between the vacuum leveland the Fermi level of the electrode. The ionization potential isdefined as the difference between the vacuum level and the HOMO, and theelectron affinity is defined as the difference between the vacuum leveland the LUMO. In the following description, the values of the workfunction, the ionization potential, and the electron affinity may bedenoted by WF, IP, and EA, respectively.

Examples of the structures of the photoelectric conversion layer 23A,the hole blocking layer 20 h, and the electron blocking layer 20 e willbe described in detail.

Photoelectric Conversion Layer

The photoelectric conversion layer 23A contains, for example, tinnaphthalocyanine represented by general formula (1) below (hereinaftermay be referred to simply as “tin naphthalocyanine”).

In general formula (1), R¹ to R²⁴ each independently represent ahydrogen atom or a substituent. The substituent is not limited to aspecific substituent. The substituent may be selected from a deuteriumatom, halogen atoms, alkyl groups (including cycloalkyl groups,bicycloalkyl groups, and tricycloalkyl groups), alkenyl groups(including cycloalkenyl groups and bicycloalkenyl groups), alkynylgroups, allyl groups, heterocyclic groups, a cyano group, a hydroxygroup, a nitro group, a carboxy group, alkoxy groups, allyloxy groups,silyloxy groups, heterocyclic oxy groups, acyloxy groups, a carbamoyloxygroup, alkoxycarbonyloxy groups, allyloxycarbonyloxy groups, aminogroups (including an anilino group), an ammonio group, acylamino groups,an aminocarbonylamino group, alkoxycarbonylamino groups,allyloxycarbonylamino groups, a sulfamoylamino group, alkylsulfonylaminogroups, allylsulfonylamino groups, a mercapto group, alkylthio groups,allylthio groups, heterocyclic thio groups, a sulfamoyl group, a sulfogroup, alkylsulfinyl groups, allylsulfinyl groups, alkylsulfonyl groups,allylsulfonyl groups, acyl groups, allyloxycarbonyl groups,alkoxycarbonyl groups, a carbamoyl group, allylazo groups, heterocyclicazo groups, an imido group, phosphino groups, phosphinyl groups,phosphinyloxy groups, phosphinylamino groups, a phosphono group, silylgroups, a hydrazino group, a ureido group, a borate group (—B(OH)₂), aphosphate group (—OPO(OH)₂), a sulfate group (—OSO₃H), and otherwell-known substituents.

A commercial product may be used as the tin naphthalocyanine representedby general formula (1) above. Alternatively, as shown in, for example,Japanese Unexamined Patent Application Publication No. 2010-232410, thetin naphthalocyanine represented by general formula (1) above can besynthesized using a naphthalene derivative represented by generalformula (2) below as a starting material. R²⁵ to R³⁰ in general formula(2) may be selected from the same substituents as those for R¹ to R²⁴ ingeneral formula (1).

In the tin naphthalocyanine represented by general formula (1) above, itis beneficial, in terms of ease of controlling the cohesion state of themolecules, that at least eight of R¹ to R²⁴ are each a hydrogen atom ora deuterium atom. It is more beneficial that at least sixteen of R¹ toR²⁴ are each a hydrogen atom or a deuterium atom, and it is still morebeneficial that all of R¹ to R²⁴ are each a hydrogen atom or a deuteriumatom. Tin naphthalocyanine represented by formula (3) below isadvantageous in terms of ease of synthesis.

The tin naphthalocyanine represented by general formula (1) aboveexhibits absorption in the wavelength range of from about 200 nm to1,100 nm inclusive. The absorption peak of tin naphthalocyanine can belocated at a wavelength of about 940 nm. The tin naphthalocyaninerepresented by formula (3) above has an absorption peak at a wavelengthof about 870 nm as shown in FIG. 5. FIG. 5 is an example of theabsorption spectrum in a photoelectric conversion layer containing thetin naphthalocyanine represented by formula (3) above. The quantumefficiency of the photoelectric conversion layer containing the tinnaphthalocyanine represented by formula (3) at a wavelength of 900 nmcan be about 10 times higher than that of silicon. In the measurement ofthe absorption spectrum, a sample in which the photoelectric conversionlayer (thickness: 30 nm) was stacked on a quartz substrate was used.

As can be seen from FIG. 5, the photoelectric conversion layer formedfrom a material containing the tin naphthalocyanine exhibits absorptionin the near infrared region. Specifically, by selecting the materialcontaining the tin naphthalocyanine as the material forming thephotoelectric conversion layer 23A, a photosensor capable of detectingnear infrared rays can be obtained. In this embodiment of the presentdisclosure, by using an appropriate material suitable for an intendeddetection wavelength range, a photosensor having sensitivity in thedesired wavelength range can be obtained. For example, P3HT(poly(3-hexylthiophene-2,5-diyl)), which is an example of an organicp-type semiconductor compound, has an absorption peak at a wavelength of550 nm, and copper phthalocyanine has absorption peaks at wavelengths of620 nm and 700 nm.

No particular limitation is imposed on the material for forming thephotoelectric conversion layer 23A so long as the material can generateelectric charges by absorption of light. The photoelectric conversionlayer 23A may be formed from an organic p-type semiconductor (compound)described later or may be formed from an organic n-type semiconductor(compound) described later. Alternatively, a combination of an organicp-type semiconductor (compound) and an organic n-type semiconductor(compound) may be used to form the photoelectric conversion layer 23A.The photoelectric conversion layer 23A may contain an inorganicsemiconductor material such as amorphous silicon. The photoelectricconversion layer 23A may include a layer formed from an organic materialand a layer formed from an inorganic material.

FIG. 6 shows an example of the structure of a photodetection elementincluding a photoelectric conversion layer formed using an organicsemiconductor material containing the tin naphthalocyanine representedby general formula (1) above. A dielectric structure 2B in thephotodetection element 10B shown in FIG. 6 includes a hole blockinglayer 20 h, a photoelectric conversion layer 23B, and an electronblocking layer 20 e. In the structure exemplified in FIG. 6, the holeblocking layer 20 h is disposed between a first electrode 21 and thephotoelectric conversion layer 23B, and the electron blocking layer 20 eis disposed between the photoelectric conversion layer 23B and a secondelectrode 22.

The photoelectric conversion layer 23B contains at least one of a p-typesemiconductor and an n-type semiconductor. In the structure exemplifiedin FIG. 6, the photoelectric conversion layer 23B includes a p-typesemiconductor layer 230 p, an n-type semiconductor layer 230 n, and amixed layer 230 h sandwiched between the p-type semiconductor layer 230p and the n-type semiconductor layer 230 n. The p-type semiconductorlayer 230 p is disposed between the hole blocking layer 20 h and themixed layer 230 h and functions as a photoelectric conversion layerand/or a hole transport layer. The n-type semiconductor layer 230 n isdisposed between the mixed layer 230 h and the electron blocking layer20 e and functions as a photoelectric conversion layer and/or anelectron transport layer. As described later, the mixed layer 230 hcontains a p-type semiconductor and an n-type semiconductor.

The p-type semiconductor layer 230 p and the n-type semiconductor layer230 n contain an organic p-type semiconductor and an organic n-typesemiconductor, respectively. The photoelectric conversion layer 23B maycontain an organic photoelectric conversion material containing the tinnaphthalocyanine represented by general formula (1) above and at leastone of an organic p-type semiconductor and an organic n-typesemiconductor.

The organic p-type semiconductor (compound) is an electron-donatingorganic semiconductor (compound) typified mainly by a hole transportorganic compound and is an organic compound having the property ofeasily donating electrons. More specifically, when two organic materialsin contact with each other are used, one of the organic materials thathas a lower ionization potential is an organic p-type semiconductor(compound). Therefore, any organic compound having the ability to donateelectrons can be used as the electron-donating organic compound.Examples of the organic compound that can be used include triallylaminecompounds, benzidine compounds, pyrazoline compounds, styrylaminecompounds, hydrazone compounds, triphenylmethane compounds, carbazolecompounds, polysilane compounds, thiophene compounds such as P3HT,phthalocyanine compounds such as copper phthalocyanine, cyaninecompounds, merocyanine compounds, oxonol compounds, polyamine compounds,indole compounds, pyrrole compounds, pyrazole compounds, polyarylenecompounds, condensed aromatic carbocyclic compounds (naphthalenederivatives, anthracene derivatives, phenanthrene derivatives, tetracenederivatives, pyrene derivatives, perylene derivatives, and fluoranthenederivatives), and metal complexes containing a nitrogen-containingheterocyclic compound as a ligand. The electron-donating organicsemiconductor is not limited to these compounds, and any other organiccompound that has a lower ionization potential than an organic compoundused as the n-type (electron-accepting) compound can be used as theelectron-donating organic semiconductor, as described above. The tinnaphthalocyanine described above is an example of the organic p-typesemiconductor material.

The organic n-type semiconductor (compound) is an electron-acceptingorganic semiconductor (compound) typified mainly by an electrontransport organic compound and is an organic compound having theproperty of easily accepting electrons. More specifically, when twoorganic materials in contact with each other are used, one of theorganic materials that has a higher electron affinity is an organicn-type semiconductor (compound). Therefore, any organic compound havingthe ability to accept electrons can be used as the electron-acceptingorganic compound. Examples of the organic compound that can be usedinclude fullerenes, fullerene derivatives such as phenyl-C₆₁-butyricacid methyl ester (PCBM), condensed aromatic carbocyclic compounds(naphthalene derivatives, anthracene derivatives, phenanthrenederivatives, tetracene derivatives, pyrene derivatives, perylenederivatives, and fluoranthene derivatives), 5- to 7-membered nitrogen,oxygen, and/or sulfur atom-containing heterocyclic compounds (such aspyridine, pyrazine, pyrimidine, pyridazine, triazine, quinoline,quinoxaline, quinazoline, phthalazine, cinnoline, isoquinoline,pteridine, acridine, phenazine, phenanthroline, tetrazole, pyrazole,imidazole, thiazole, oxazole, indazole, benzimidazole, benzotriazole,benzoxazole, benzothiazole, carbazole, purine, triazolopyridazine,triazolopyrimidine, tetrazaindene, oxadiazole, imidazopyridine,pyrrolopyridine, thiadiazolopyridine, dibenzazepine, andtribenzazepine), polyarylene compounds, fluorene compounds,cyclopentadiene compounds, silyl compounds, perylenetetracarboxylicdiimide (PTCDI) compounds, and metal complexes containing anitrogen-containing heterocyclic compound as a ligand. Theelectron-accepting organic semiconductor is not limited to thesecompounds, and any other organic compound that has a higher electronaffinity than an organic compound used as the p-type (electron-donating)compound can be used as the electron-accepting organic semiconductor, asdescribed above.

When the dielectric structure 2B has the photoelectric conversion layer23B including the p-type semiconductor layer 230 p and the n-typesemiconductor layer 230 n as exemplified in FIG. 6, holes and electronsgenerated by photoelectric conversion can be easily separated from eachother. Therefore, when the photoelectric conversion layer 23B includingthe p-type semiconductor layer 230 p and the n-type semiconductor layer230 n is used, the efficiency of charge separation is improved, and achange in the intensity of incident light can cause a larger change inpermittivity.

The mixed layer 230 h may be, for example, a bulk heterojunctionstructure layer containing a p-type semiconductor and an n-typesemiconductor. When the mixed layer 230 h is formed as a layer havingthe bulk heterojunction structure, the tin naphthalocyanine representedby general formula (1) above may be used as the p-type semiconductormaterial. The n-type semiconductor material used may be a fullereneand/or a fullerene derivative. The details of the bulk heterojunctionstructure are described in Japanese Patent No. 5553727. The entiredisclosure of Japanese Patent No. 5553727 is incorporated herein forreference purposes.

Hole Blocking Layer

The material used to form the hole blocking layer 20 h may be an n-typesemiconductor or an electron transport organic compound. Examples ofsuch materials include: organic materials and organic-metal compoundssuch as fullerenes, e.g., C₆₀ and C₇₀, fullerene derivatives, e.g.,indene-C₆₀ bisadduct (ICBA), carbon nanotubes and derivatives thereof,oxadiazole derivatives, e.g., OXD-7(1,3-bis(4-tert-butylphenyl-1,3,4-oxadiazolyl)phenylene),anthraquinodimethane derivatives, diphenylquinone derivatives,bathocuproine (BCP), bathophenanthroline and derivatives thereof,distyrylarylene derivatives, triazole compounds, silole compounds, atris(8-hydroxyquinolinato)aluminum complex, abis(4-methyl-8-quinolinato)aluminum complex, acetylacetonate complexes,copper phthalocyanine, 3,4,9,10-perylenetetracarboxylic dianhydride(PTCDA), and Alq; and inorganic materials such as MgAg and MgO. Thematerial used to form the hole blocking layer 20 h may be selected fromthe above materials in consideration of the ionization potential of thematerial forming the photoelectric conversion layer 23A (or the p-typesemiconductor layer 230 p in the photoelectric conversion layer 23B).

In a structure in which light enters the photoelectric conversion layer23B (or the photoelectric conversion layer 23A) from the first electrode21 side, it is beneficial when the transmittance of the hole blockinglayer 20 h in the intended detection wavelength range is high. Forexample, the hole blocking layer 20 h may be reduced in thickness. Thehole blocking layer 20 h may have a thickness within the range of, forexample, from 5 nm to 50 nm inclusive. sElectron Blocking Layer

The material used to form the electron blocking layer 20 e may be ap-type semiconductor or a hole transport organic compound. Examples ofsuch materials include aromatic diamine compounds such as TPD(N,N′-bis(3-methylphenyl)-(1,1′-biphenyl)-4,4′-diamine) and α-NPD(4,4′-bis[N-(naphthyl)-N-phenyl-amino]biphenyl), oxazole, oxadiazole,triazole, imidazole, imidazolone, stilbene derivatives, pyrazolinederivatives, tetrahydroimidazole, polyarylalkanes, butadiene, m-MTDATA(4,4′,4′-tris(N-(3-methylphenyl)N-phenylamino)triphenylamine), perylene,porphyrin compounds such as porphine, copper tetraphenylporphine,phthalocyanine, copper phthalocyanine, and titanium phthalocyanineoxide, triazole derivatives, oxadiazole derivatives, imidazolederivatives, polyarylalkane derivatives, pyrazoline derivatives,pyrazolone derivatives, phenylenediamine derivatives, allylaminederivatives, amino-substituted chalcone derivatives, oxazolederivatives, styrylanthracene derivatives, fluorenone derivatives,hydrazone derivatives, and silazane derivatives. The material used toform the electron blocking layer 20 e may be: polymers ofphenylenevinylene, fluorene, carbazole, indole, pyrene, pyrrole,picoline, thiophene, acetylene, and diacetylene; and derivativesthereof. The material used to form the electron blocking layer 20 e isselected from the above materials in consideration of the electronaffinity of the photoelectric conversion layer 23A (or the n-typesemiconductor layer 230 n in the photoelectric conversion layer 23B).

In a structure in which light enters the photoelectric conversion layer23B (or the photoelectric conversion layer 23A) from the secondelectrode 22 side, it is beneficial when the transmittance of theelectron blocking layer 20 e in the intended detection wavelength rangeis high. For example, the electron blocking layer 20 e may be reduced inthickness. The electron blocking layer 20 e may have a thickness withinthe range of, for example, from 5 nm to 50 nm inclusive.

Other Structural Examples of Photodetection Element

By selecting an appropriate combination of the materials of the firstelectrode 21, the photoelectric conversion layer (the photoelectricconversion layer 23A or 23B), and the second electrode 22, one of thehole blocking layer 20 h and the electron blocking layer 20 e can beomitted. Examples of such a structure will next be described.

FIG. 7 is an exemplary energy diagram of a photodetection element inwhich the hole blocking layer 20 h and a photoelectric conversion layer23C are disposed between the first electrode 21 and the second electrode22. As illustrated, in this example, the photoelectric conversion layer23C is adjacent to the second electrode 22 to which the second voltageis applied. Specifically, FIG. 7 shows a structural example in which theelectron blocking layer 20 e is omitted. In the example described here,the photoelectric conversion layer 23C has a heterojunction structurebetween the p-type semiconductor layer 230 p and the n-typesemiconductor layer 230 n. Of course, the photoelectric conversion layer23C may have a bulk heterojunction structure.

In the structure exemplified in FIG. 7, as in the photodetection element10A described with reference to FIGS. 2 and 3, the hole blocking layer20 h suppresses movement of holes from the photoelectric conversionlayer 23C to the first electrode 21. In the structure exemplified inFIG. 7, the difference between the LUMO of the hole blocking layer 20 hand the Fermi level of the first electrode 21 is large, and therefore apotential barrier for electrons is formed between the first electrode 21and the hole blocking layer 20 h. The potential barrier suppressesmovement of electrons from the first electrode 21 to the hole blockinglayer 20 h. In other words, transport of electrons from the firstelectrode 21 to the hole blocking layer 20 h is suppressed without usingan electron blocking layer.

In the structure in which the photoelectric conversion layer (thephotoelectric conversion layer 23C in this case) and an electrode (thesecond electrode 22 in this case) are disposed adjacent to each other,it is known that, when the difference between the work function of theelectrode and the ionization potential of the organic film adjacent tothe electrode is large, holes are unlikely to enter the organic filmfrom the electrode. In the structure exemplified in FIG. 7, theionization potential of the photoelectric conversion layer 23C is higherthan the work function of the second electrode 22, and the differencebetween the HOMO of the photoelectric conversion layer 23C and the Fermilevel of the second electrode 22 is relatively large. Therefore, thepotential barrier between the photoelectric conversion layer 23C and thesecond electrode 22 suppresses injection of holes from the secondelectrode 22 into the photoelectric conversion layer 23C.

As described above, also by suppressing movement of positive charges ornegative charges (holes in this case) generated by photoelectricconversion to an electrode (the first electrode 21 in this case), thecharges generated by photoelectric conversion can be retained within thephotoelectric conversion layer 23C. Specifically, even though theelectron blocking layer 20 e is not provided, the permittivity can bechanged in response to irradiation with light when the materials of thefirst electrode 21, the hole blocking layer 20 h, the photoelectricconversion layer 23C, and the second electrode 22 are appropriatelyselected such that the relative relations among the energies of thecomponents of the photodetection element are as shown in FIG. 7.

One example of the combination of the materials that can satisfy therelative relations among the energies of the components of thephotodetection element in FIG. 7 is as follows.

First electrode 21: ITO (WF: 4.7 eV)

Hole blocking layer 20 h: ICBA (IP: 6.5 eV, EA: 3.7 eV)

p-Type semiconductor layer 230 p: copper phthalocyanine (IP: 5.2 eV, EA:3.5 eV)

n-Type semiconductor layer 230 n: C₆₀ (IP: 6.2 eV, EA: 4.5 eV)

Second electrode 22: Al (WF: 4.2 eV)

FIG. 8 schematically shows the relative relations among the energiesobtained by the above combination. In FIG. 8, an arrow φ1 represents apotential barrier for electrons between the hole blocking layer 20 h andthe first electrode 21, and an arrow φ2 represents a potential barrierfor holes between the n-type semiconductor layer 230 n and the secondelectrode 22. An arrow φ3 represents a potential barrier for holesbetween the p-type semiconductor layer 230 p and the hole blocking layer20 h. Of course, the above combination is merely an example. Forexample, P3HT, tin naphthalocyanine, etc. may be used instead of copperphthalocyanine exemplified as the material of the p-type semiconductorlayer 230 p.

FIG. 9 is an exemplary energy diagram of a photodetection element inwhich the photoelectric conversion layer 23C and the electron blockinglayer 20 e are disposed between the first electrode 21 and the secondelectrode 22. As illustrated, in this example, the photoelectricconversion layer 23C is adjacent to the first electrode 21 to which thefirst voltage is applied. Specifically, FIG. 9 shows a structuralexample in which the hole blocking layer 20 h is omitted.

In the example illustrated, as in the photodetection element 10Adescribed with reference to FIGS. 2 and 3, the electron blocking layer20 e suppresses movement of electrons from the photoelectric conversionlayer 23C to the second electrode 22. In the structure exemplified inFIG. 9, the difference between the HOMO of the electron blocking layer20 e and the Fermi level of the second electrode 22 is large, and apotential barrier for holes is formed between the electron blockinglayer 20 e and the second electrode 22. This potential barriersuppresses movement of holes from the second electrode 22 to theelectron blocking layer 20 e. In other words, transport of holes fromthe second electrode 22 to the electron blocking layer 20 e issuppressed without using a hole blocking layer.

In the structure in which the photoelectric conversion layer (thephotoelectric conversion layer 23C in this case) and an electrode (thefirst electrode 21 in this case) are disposed adjacent to each other,when the difference between the work function of the electrode and theelectron affinity of the organic film adjacent to the electrode islarge, electrons are unlikely to be injected into the organic film fromthe electrode. In the structure exemplified in FIG. 9, the electronaffinity of the photoelectric conversion layer 23C is lower than thework function of the first electrode 21, and the difference between theFermi level of the first electrode 21 and the LUMO of the photoelectricconversion layer 23C is relatively large. Therefore, a potential barrieris formed between the first electrode 21 and the photoelectricconversion layer 23C. This potential barrier suppresses injection ofelectrons from the first electrode 21 into the photoelectric conversionlayer 23C. As described above, even though the hole blocking layer 20 his not provided, the permittivity can be changed in response toirradiation with light when the materials of the first electrode 21, thephotoelectric conversion layer 23C, the electron blocking layer 20 e,and the second electrode 22 are appropriately selected such that therelative relations among the energies of the components of thephotodetection element are as shown in FIG. 9.

One example of the combination of the materials of the first electrode21, the photoelectric conversion layer 23C, the electron blocking layer20 e, and the second electrode 22 that are combined so as to satisfy therelative relations among the energies of the components of thephotodetection element in FIG. 9 is as follows.

First electrode 21: ITO (WF: 4.7 eV)

p-Type semiconductor layer 230 p: copper phthalocyanine (IP: 5.2 eV, EA:3.5 eV)

n-Type semiconductor layer 230 n: C₆₀ (IP: 6.2 eV, EA: 4.5 eV)

Electron blocking layer 20 e: perylene (IP: 5.3 eV, EA: 2.3 eV)

Second electrode 22: Al (WF: 4.2 eV)

FIG. 10 schematically shows the relative relations among the energiesobtained by the above combination. In FIG. 10, an arrow φ5 represents apotential barrier for electrons between the first electrode 21 and thep-type semiconductor layer 230 p. An arrow φ6 represents a potentialbarrier for holes between the electron blocking layer 20 e and thesecond electrode 22, and an arrow φ7 represents a potential barrier forelectrons between the n-type semiconductor layer 230 n and the electronblocking layer 20 e. P3HT, tin naphthalocyanine, etc. may be usedinstead of copper phthalocyanine exemplified as the material of thep-type semiconductor layer 230 p. Copper phthalocyanine may be usedinstead of perylene exemplified as the material of the electron blockinglayer 20 e.

As described above, the photodetection element in which the holeblocking layer 20 h or the electron blocking layer 20 e is omitted canalso suppress movement of electric charges generated by photoelectricconversion to the electrodes. In other words, the same effects as thoseof the photodetection element having both the hole blocking layer 20 hand the electron blocking layer 20 e can be obtained using the simplerstructures. It should be noted that, in the photodetection element inwhich one of the hole blocking layer 20 h and the electron blockinglayer 20 e is disposed in the dielectric structure, the position of theinterposed blocking layer (the hole blocking layer 20 h or the electronblocking layer 20 e) is determined according to which of the twoelectrodes is at a higher electric potential under the application ofvoltage.

Second Embodiment of Photosensor

In terms of suppressing movement of electric charges generated byphotoelectric conversion to the electrodes, an insulating layer thatdoes not allow holes and electron to pass through may be used instead ofthe hole blocking layer 20 h and/or the electron blocking layer 20 e. Adescription will be given of an example of the structure in which aninsulating layer is disposed between a photoelectric conversion layerand electrodes.

FIG. 11 shows the outline of an exemplary structure of a photosensoraccording to a second embodiment of the present disclosure. Thephotosensor 100C shown in FIG. 11 includes: a photodetection element 10Cincluding a dielectric structure 2C disposed between a first electrode21 and a second electrode 22; and a voltage supply circuit 12. Thedielectric structure 2C includes an insulating layer 29 a and aninsulating layer 29 b. As illustrated, the insulating layer 29 a isdisposed between the first electrode 21 and the photoelectric conversionlayer 23C. The insulating layer 29 b is disposed between thephotoelectric conversion layer 23C and the second electrode 22.

FIG. 12 is an exemplary energy diagram of the photodetection element10C. In FIG. 12, the base of the leftmost one of three rectanglesrepresents the upper edge of the valence band of the insulating layer 29a, and the side opposite to the base represents the bottom of itsconduction band. Similarly, the rightmost rectangle in FIG. 12schematically shows the energy levels of the upper edge of the valenceband of the insulating layer 29 b and the bottom of its conduction band.In the following description, the difference between the upper edge of avalence band and the vacuum level and the difference between the bottomof a conduction band and the vacuum level may be represented by VB andCB, respectively.

By disposing the insulating layer 29 a between the first electrode 21and the photoelectric conversion layer 23C, movement of electric chargesbetween the first electrode 21 and the photoelectric conversion layer23C can be suppressed even when a voltage is applied between the firstelectrode 21 and the second electrode 22. By disposing the insulatinglayer 29 b between the second electrode 22 and the photoelectricconversion layer 23C, movement of electric charges between the secondelectrode 22 and the photoelectric conversion layer 23C can besuppressed. Therefore, the electric charges generated by photoelectricconversion are suppressed from migrating to the electrodes (the firstelectrode 21 and/or the second electrode 22) and can be used as electriccharges contributing to a change in the permittivity of the dielectricstructure 2C. The “insulating layers” as used herein are distinguishedfrom the hole blocking layer 20 h and the electron blocking layer 20 ebecause the insulating layers block the movement of both the positiveand negative charges irrespective of the direction of the electric fieldapplied from the outside. In other words, the “insulating layers” asused herein suppress both the positive and negative charges frommigrating from the electrodes to the photoelectric conversion layer andfrom migrating from the photoelectric conversion layer to theelectrodes.

The material used to form the insulating layers 29 a and 29 b may be,for example, an oxide such as SiO₂, Al₂O₃, ZrO₂, HfO₂, or Y₂O₃ or aresin such as polymethyl methacrylate (PMMA), polyimide, parylene(registered trademark), or polystyrene. The same material may be used toform the insulating layers 29 a and 29 b, or different materials may beused. A silicon oxynitride film (SiON film) generally used for siliconsemiconductors may be used for the insulating layer 29 a and/or theinsulating layer 29 b. It is beneficial that a so-calledhigh-permittivity material (referred to also as a high-k material andhaving a relative permittivity of typically more than 3.9) is used toform the insulating layer 29 a and/or the insulating layer 29 b. Thethicknesses of the insulating layer 29 a and the insulating layer 29 bmay be appropriately set according to the electric conductivities of theinsulating layer 29 a and the insulating layer 29 b.

In the structure exemplified in FIGS. 11 and 12, the insulating layer 29a is disposed between the first electrode 21 and the photoelectricconversion layer 23C. Moreover, the insulating layer 29 b is disposedbetween the photoelectric conversion layer 23C and the second electrode22. Therefore, during operation of the photosensor 100C, any one of thefirst electrode 21 and the second electrode 22 may be at a higherpotential than the other. Specifically, the structure exemplified inFIG. 11 has an advantage in that less restrictions are imposed on thematerial of the first electrode 21 and the material of the secondelectrode 22. For example, when the second electrode 22 is a transparentelectrode, the material used for the second electrode 22 may be atransparent conductive oxide (TCO) such as ITO, IZO, AZO, FTO, SnO₂,TiO₂, or ZnO₂, a carbon nanotube, graphene, etc. When the firstelectrode 21 is a transparent electrode, the material used for thesecond electrode 22 may be Al, TiN, Cu, TaN, etc. The material used forthe first electrode 21 may be selected from the same materials as thosefor the second electrode 22. For example, the material used for thefirst electrode 21 may be Al, TiN, Cu, TaN, ITO, etc.

Other Structural Examples of Photodetection Element

As described below, one of the insulating layers 29 a and 29 b can beomitted by selecting an appropriate combination of the materials of thefirst electrode 21, the photoelectric conversion layer 23C (or thephotoelectric conversion layer 23A or 23B), and the second electrode 22.

FIG. 13 is an exemplary energy diagram of a photodetection element inwhich the insulating layer 29 a and the photoelectric conversion layer23C are disposed between the first electrode 21 and the second electrode22. As illustrated, in this example, the photoelectric conversion layer23C is adjacent to the second electrode 22 to which the second voltageis applied. Specifically, FIG. 13 shows a structural example in whichthe insulating layer 29 b is omitted.

In the structure exemplified in FIG. 13, the insulating layer 29 asuppresses movement of holes from the photoelectric conversion layer 23Cto the first electrode 21 and movement of electrons from the firstelectrode 21 to the photoelectric conversion layer 23C. In this example,the ionization potential of the photoelectric conversion layer 23C isset to be larger than the work function of the second electrode 22.Therefore, injection of holes from the second electrode 22 into thephotoelectric conversion layer 23C is suppressed by the potentialbarrier between the photoelectric conversion layer 23C and the secondelectrode 22. In this case, part of electric charges (e.g., holes)generated by photoelectric conversion can be retained within thephotoelectric conversion layer 23C and can be utilized as electriccharges contributing to a change in the permittivity of thephotoelectric conversion layer 23C. As described above, even though theinsulating layer 29 b is not provided between the photoelectricconversion layer 23C and the second electrode 22, movement of electriccharges generated by photoelectric conversion to the electrodes can besuppressed by appropriately selecting the materials of the firstelectrode 21, the insulating layer 29 a, the photoelectric conversionlayer 23C, and the second electrode 22 such that the relative relationsamong the energies of the components of the photodetection element areas shown in FIG. 13.

One example of the combination of the materials that can satisfy therelative relations among the energies of the components of thephotodetection element in FIG. 13 is as follows.

First electrode 21: ITO (WF: 4.7 eV)

Insulating layer 29 a: Al₂O₃ (VB: 10.0 eV, CB: 1.2eV)

p-Type semiconductor layer 230 p: copper phthalocyanine (IP: 5.2 eV, EA:3.5 eV)

n-Type semiconductor layer 230 n: C₆₀ (IP: 6.2 eV, EA: 4.5 eV)

Second electrode 22: Al (WF: 4.2 eV)

FIG. 14 schematically shows the relative relations among the energiesobtained by the above combination. The material used for the secondelectrode 22 may be a metal having a work function of from about 4.1 eVto about 4.3 eV inclusive. Therefore, instead of Al exemplified as thematerial of the second electrode 22, Ti, Ta, Ag, etc. may be used. Thematerial used for the n-type semiconductor layer 230 n adjacent to thesecond electrode 22 may be a material having an ionization potential ofabout 5 eV or more. Instead of Al₂O₃ exemplified as the material of theinsulating layer 29 a, SiO₂, ZrO₂, HfO₂, Y₂O₃, etc. may be used.

FIG. 15 is an exemplary energy diagram of a photodetection element inwhich the photoelectric conversion layer 23C and the insulating layer 29b are disposed between the first electrode 21 and the second electrode22. As illustrated, in this example, the photoelectric conversion layer23C is adjacent to the first electrode 21 to which the first voltage isapplied. Specifically, FIG. 15 shows an example in which the insulatinglayer 29 a is omitted.

In the structure exemplified in FIG. 15, the insulating layer 29 bblocks movement of electrons from the photoelectric conversion layer 23Cto the second electrode 22 and movement of holes from the secondelectrode 22 to the photoelectric conversion layer 23C. In this example,the electron affinity of the photoelectric conversion layer 23C is setto be lower than the work function of the first electrode 21. In thiscase, injection of electrons from the first electrode 21 into thephotoelectric conversion layer 23C is suppressed by the potentialbarrier between the first electrode 21 and the photoelectric conversionlayer 23C. Therefore, also in the above structure, part of electriccharges (e.g., electrons) generated by photoelectric conversion can beretained within the photoelectric conversion layer 23C and can be usedas electric charges contributing to a change in the permittivity of thephotoelectric conversion layer 23C. As described above, even though theinsulating layer 29 a is not provided between the first electrode 21 andthe photoelectric conversion layer 23C, movement of electric chargesgenerated by photoelectric conversion to the electrodes can besuppressed by appropriately selecting the materials of the firstelectrode 21, the photoelectric conversion layer 23C, the insulatinglayer 29 b, and the second electrode 22 such that the relative relationsamong the energies of the components of the photodetection element areas shown in FIG. 15.

One example of the combination of the materials that can satisfy therelative relations among the energies of the components of thephotodetection element in FIG. 15 is as follows.

First electrode 21: Au (WF: 4.9 eV)

p-Type semiconductor layer 230 p: copper phthalocyanine (IP: 5.2 eV, EA:3.5 eV)

n-Type semiconductor layer 230 n: C₆₀ (IP: 6.2 eV, EA: 4.5 eV)

Insulating layer 29 b: Al₂O₃ (VB: 10.0 eV, CB: 1.2 eV)

Second electrode 22: ITO (WF: 4.7 eV)

FIG. 16 schematically shows the relative relations among the energiesobtained by the above combination. The material used for the firstelectrode 21 may be a metal having a work function of about 4.8 eV ormore. For example, instead of Au exemplified as the material of thefirst electrode 21, Pt, Ni, ITO, etc. may be used.

EXAMPLES

An example of the change in the permittivity of a photoelectricconversion layer due to light irradiation will be described withreference to an Example. FIG. 17 schematically shows the structure of aphotodetection element used for measurement of the change inpermittivity. The photodetection element 10D having the structure shownin FIG. 17 was produced using the following procedure.

First, a glass substrate 2GL was prepared. Next, ITO was deposited onthe glass substrate 2GL by sputtering to thereby form an ITO electrode(thickness: 50 nm) serving as a second electrode 22. Next, atomic layerdeposition (ALD) was used to form a HfO₂ layer (thickness: 30 nm)serving as an insulating layer 29 b on the second electrode 22. Then tinnaphthalocyanine and C₆₀ were co-evaporated to form a co-evaporatedlayer (thickness: 150 nm) serving as a photoelectric conversion layer23D on the insulating layer 29 b.

Next, ALD was used to form an Al₂O₃ layer (thickness: 30 nm) serving asan insulating layer 29 a on the photoelectric conversion layer 23D. Thensputtering was used to deposit Al on the insulating layer 29 a tothereby form an Al electrode (thickness: 80 nm) serving as a firstelectrode 21. Through the above steps, a photodetection element 10Dhaving the structure shown in FIG. 17 was obtained. The shape of thephotoelectric conversion layer 23D was a rectangle with 1 mm sides whenviewed in a direction normal to the glass substrate 2GL.

In this example, an LED light source (wavelength: 940 nm, rated powerconsumption: about 70 mW) was used. As schematically shown in FIG. 17, ameasuring apparatus 300 was connected to the first electrode 21 and thesecond electrode 22 to apply a potential difference of 4 V between thefirst electrode 21 and the second electrode 22. In this state, thecapacitance value of a dielectric structure 2D between the firstelectrode 21 and the second electrode 22 was measured. To measure thecapacitance value, a semiconductor device parameter analyzer B1500A(measurement frequency: 1 kHz, amplitude: 0.1 V) manufactured byKeysight was used. During the measurement, a LOW side of a probe of themeasuring apparatus was brought into contact with the first electrode21, and a HIGH side of the probe was brought into contact with thesecond electrode 22.

FIG. 18 shows the results of the measurement of the capacitance value ofthe dielectric structure 2D. In FIG. 18, open squares (□) show theresults of the capacitance value measurement when the photoelectricconversion layer 23D was not irradiated with light (LED light source:off, dark condition). Open triangles (Δ) show the results of thecapacitance value measurement when the photoelectric conversion layer23D was irradiated with light (LED light source: on). As shown in FIG.18, the capacitance value without light irradiation was about 2 μF, andthe capacitance value under light irradiation was about 6.3 μF.Therefore, in this example, when the photoelectric conversion layer 23Dwas irradiated with light, the capacitance value of the dielectricstructure 2D was increased by a factor of about 3 as compared to that inthe dark condition.

Changes in the capacitance value of the dielectric structure 2D weremeasured with a potential difference of 4 V applied between the firstelectrode 21 and the second electrode 22 while the LED light source wasrepeatedly turned on and off at one second intervals. In FIG. 18, opendiamonds (⋄) show the results of the capacitance value measurement whenthe LED light source was repeatedly turned on and off at one secondintervals. As shown in FIG. 18, when light enters the photoelectricconversion layer 23D, the capacitance value of the dielectric structure2D increases steeply. When the LED light source is turned off, thecapacitance value of the dielectric structure 2D decreases steeply.

As described above, according to this embodiment of the presentdisclosure, a photosensor in which the capacitance value between itselectrodes changes in response to a change in illuminance can beobtained.

Specific Examples of Device Structure

Next, referring to the drawings, a description will be given of specificexamples of the device structure of the photodetection element capableof generating a signal that corresponds to a change in permittivity dueto irradiation with light.

FIG. 19 shows an example of the device structure of the photodetectionelement. The photodetection element 10E shown in FIG. 19 is supported bya substrate 2. The substrate 2 used may be, for example, a siliconsubstrate having an oxide film on its surface, a glass substrate, or apolyimide substrate. In the example illustrated, a second electrode 22is disposed on the substrate 2.

In the structure exemplified in FIG. 19, a dielectric structure 2Edisposed between a first electrode 21 and the second electrode 22includes barrier layers B1 and B2 and a photoelectric conversion layer23A. The barrier layer B1 disposed between the first electrode 21 andthe photoelectric conversion layer 23A may be the hole blocking layer 20h described above or the insulating layer 29 a described above.Specifically, the barrier layer B1 is a layer having the function ofsuppressing at least transport of holes from the photoelectricconversion layer (the photoelectric conversion layer 23A in this case)to the first electrode 21. The barrier layer B2 disposed between thephotoelectric conversion layer 23A and the second electrode 22 may bethe electron blocking layer 20 e described above or the insulating layer29 b described above. Specifically, the barrier layer B2 is a layerhaving the function of suppressing at least transport of electrons fromthe photoelectric conversion layer (the photoelectric conversion layer23A in this case) to the second electrode 22.

By employing the capacitor structure exemplified in FIG. 19, lightentering the photoelectric conversion layer 23A can be detected as achange in the capacitance value between the first electrode 21 and thesecond electrode 22. The light may enter from the first electrode 21side or may enter from the second electrode 22 side. For example, whenthe first electrode 21 is a transparent electrode, the light may enterthe photoelectric conversion layer 23A through the first electrode 21.Alternatively, when the substrate 2 is a transparent substrate and thesecond electrode 22 is a transparent electrode, the light may enter thephotoelectric conversion layer 23A through the substrate 2 and thesecond electrode 22.

In FIG. 19, the voltage supply circuit 12 (see, for example, FIG. 2) isnot illustrated and is omitted. In the structure in which thephotodetection element (the photodetection element 10E in this case) issupported by the substrate (the substrate 2 in this case) as exemplifiedin FIG. 19, the voltage supply circuit 12 may be disposed on thesubstrate.

The change in the capacitance value between the first electrode 21 andthe second electrode 22 may be detected, for example, in the followingmanner. First, an AC voltage is applied between the electrodes 21 and22, and the change in electric current flowing between the electrodes 21and 22 is detected. Let the frequency of the AC voltage be ω, theamplitude ratio of the voltage to the current be A, the difference inphase be δ, and tan δ be D. When an equivalent circuit between theelectrodes 21 and 22 is a series circuit including a resistancecomponent and a capacitance component, the capacitance can be computedfrom the following formula.

$C_{s} = \frac{\sqrt{1 + D^{2}}}{\omega \; A}$

When the equivalent circuit between the electrodes 21 and 22 is aparallel circuit including a resistance component and a capacitancecomponent, the capacitance can be computed from the following formula.

$C_{p} = \frac{1}{\omega \; A\sqrt{1 + D^{2}}}$

In actual measurement, an appropriate one of the above two formulas canbe selected according to the structure of the element and the frequencyof the AC voltage.

A different detection method will be described with reference to FIG.22. FIG. 22 schematically shows a cross section of a photodetectorincluding the capacitor structure of the present disclosure.

In FIG. 22, a photosensor 100C includes a transistor 60 and aphotoelectric conversion unit. The transistor 60 is a field effecttransistor formed on a semiconductor substrate 20. The transistor 60includes an impurity region 20 d, an impurity region 20 s, an insulatinglayer 23 x on the semiconductor substrate, and a gate electrode 24 onthe insulating layer 23 x. The impurity region 20 d functions as a drainregion (or a source region) of the transistor 60, and the impurityregion 20 s function as the source region (or the drain region) of thetransistor 60. The impurity region 20 d is connected to a power sourceline 42, so that a prescribed voltage can be applied to the impurityregion 20 d during operation of the photodetector 1000. The insulatinglayer 23 x functions as a gate insulating layer of the transistor 60.The insulating layer 23 x is, for example, a thermally oxidized siliconfilm having a thickness of 4.6 nm.

The photoelectric conversion unit of the photosensor 100C includes apixel electrode 21, a transparent electrode 22 facing the pixelelectrode 21, and a photoelectric conversion layer 23 p sandwichedtherebetween. An insulating layer 29 a is disposed between the pixelelectrode 21 and the photoelectric conversion layer 23 p, and aninsulating layer 29 b is disposed between the photoelectric conversionlayer 23 p and the transparent electrode 22. The pixel electrode 21 isdisposed so as to be spaced apart from adjacent unit pixel cells 10C.Therefore, the pixel electrode 21 is electrically isolated from pixelelectrodes 21 of other unit pixel cells 10C. The pixel electrode 21 istypically a metal electrode or a metal nitride electrode. Examples ofthe material for forming the pixel electrode 21 include Al, Cu, Ti, TiN,Ta, TaN, Mo, Ru, and Pt. The pixel electrode 21 may be formed frompolysilicon doped with an impurity to impart electrical conductivity. Inthe above case, the pixel electrode 21 used is a TiN electrode.

For example, a material through which a smaller leakage current can flowthan through the material forming the photoelectric conversion layer 23p may be selected as the material forming the insulating layers 29 a and29 b. In this case, a silicon oxide film having a thickness of 5.4 nm isused for the insulating layers 29 a and 29 b. The silicon oxide film canbe formed by, for example, CVD.

The photoelectric conversion layer 23 p is formed so as to extend overother unit pixel cells 10C. The thickness of the photoelectricconversion layer 23 p may be, for example, about 200 nm. The transparentelectrode 22 is formed using a transparent conducting oxide (TCO) so asto extend over other unit pixel cells 10C. The transparent electrode 22is connected to a gate voltage control line (not illustrated), so that aprescribed voltage can be applied to the transparent electrode 22 duringoperation of the photodetector 1000.

In the example illustrated, the transparent electrode 22 and thephotoelectric conversion layer 23 p are disposed above an interlayerinsulating layer 50, and the pixel electrode 21 of the photoelectricconversion unit is connected to the gate electrode 24 of thecapacitance-modulated transistor 60 through a connection portion 54including part of multilayer wiring 40 and a contact plug 52.

In the example described, a first voltage applied to the impurity region20 d is 1.2 V, and a second voltage applied to the transparent electrode22 is 3.7 V. Specifically, in this example, a potential difference ofabout 2.5 V is applied between the impurity region 20 d and thetransparent electrode 22.

FIG. 23 shows the film thickness dependence of a leakage current flowingthrough the silicon oxide film when a voltage of 2.5 V is applied. Interms of maintaining the characteristics with no light irradiation, itis beneficial that the leakage current to the channel region of thecapacitance-modulated transistor 60 is 1×10⁻¹¹ A/cm² or less. As shownin FIG. 23, in the case in which a voltage of 2.5 V is applied to thesilicon oxide film, the leakage current through the silicon oxide filmcan be reduced to 1×10⁻¹¹ A/cm² or less when the thickness of thesilicon oxide film is 5.4 nm or more.

When light enters the photoelectric conversion layer 23 p, hole-electronpairs are generated in the photoelectric conversion layer 23 p, and thepermittivity of the photoelectric conversion layer 23 p changes. As thepermittivity of the photoelectric conversion layer 23 p changes, theeffective gate voltage of the capacitance-modulated transistor 60changes, and a drain current in the capacitance-modulated transistor 60changes. Therefore, the change in illuminance can be detected as, forexample, a change in voltage in a vertical signal line 46.

In another detection method, a fixed capacitor connected in series tothe electrode 21 or 22 in the capacitor structure exemplified in FIG. 19is further provided. With a constant voltage applied between twoelectrodes not used for the mutual connection between the fixedcapacitor and the electrode, an intermediate voltage between thecapacitor structure and the fixed capacitor is read, whereby the changein illuminance can be detected.

The fixed capacitor has a structure in which an insulating materialusing an oxide film, a nitride film, or an organic film is sandwichedbetween two electrodes and a change in capacitance in response to lightis small (the capacity can be regarded as a constant).

To read the change in the capacitance of the capacitor structureefficiently, it is desirable to design the capacitor structure such thatthe initial capacitance value of the capacitor structure under thecondition in which no light enters the capacitor structure is lower thanthe capacitance value of the fixed capacitor.

It is also desirable to set the positional relation between the fixedcapacitor and the capacitor structure such that the capacitor structureis disposed on the light incident side.

Let the constant voltage applied be VG, the capacitance value of thecapacitor structure be C1, and the capacitance value of the fixedcapacitor be C2. Then the intermediate voltage can be represented by aformula below. Using this formula, the change in the capacitance of thecapacitor structure due to the incident light can be read as a change involtage.

$V = {\frac{C\; 1}{{C\; 1} + {C\; 2}}{VG}}$

To read the voltage, a transistor can be used, and the signal can beread nondestructively through connection to the gate electrode side ofthe transistor.

The photodetection element in the photosensor of the present disclosurecan be configured as a three-terminal element. Other specific examplesof the device structure of the photodetection element will be describedwith reference to FIGS. 20 and 21.

FIG. 20 shows another example of the device structure of thephotodetection element. The photodetection element 10F shown in FIG. 20has a device structure similar to the device structure of thephotodetection element 10E described with reference to FIG. 19. However,the structure exemplified in FIG. 20 differs from the photodetectionelement 10E shown in FIG. 19 in that, instead of the first electrode 21,a semiconductor layer SL, an electrode Ed, and an electrode Es aredisposed on the barrier layer B1. As illustrated, the electrode Ed andthe electrode Es are disposed on the semiconductor layer SL so as to bespaced apart from each other. As can be seen from FIG. 20, thephotodetection element 10F has the device structure similar to a bottomgate thin film transistor. Examples of the material forming thesemiconductor layer SL include single-walled carbon nanotubes (SWCNTs),oxide semiconductors including In—Ga—Zn—O-based (IGZO) semiconductors,organic semiconductors such as pentacene and P3HT, and amorphoussilicon.

For example, suppose that light enters the photoelectric conversionlayer 23A through the substrate 2 and the second electrode 22. In thiscase, when the first voltage is applied to one of the electrode Ed andthe electrode Es and when the second voltage is applied to the secondelectrode 22, the permittivity of the dielectric structure 2E changes.When the permittivity of the dielectric structure 2E increases, electriccharges are induced in the semiconductor layer SL, and a current flowingbetween the electrode Ed and the electrode Es changes. Therefore, asignal corresponding to the illuminance of the light can be taken fromthe other one of the electrodes Ed and Es to which the first voltage isnot applied.

FIG. 21 shows another example of the device structure of thephotodetection element. As exemplified in FIG. 21, a device structuresimilar to a top gate thin film transistor can be used. In this example,a semiconductor layer SL is disposed so as to cover electrodes Ed and Esspaced apart from each other, and a dielectric structure 2E is disposedon the semiconductor layer SL. A first electrode 21 is disposed on thedielectric structure 2E.

When light is detected using the photodetection element 10G shown inFIG. 21, the first voltage is applied to, for example, the firstelectrode 21, and the second voltage is applied to one of the electrodeEd and the electrode Es. In this case, as in the photodetection element10F described above, a signal corresponding to the illuminance of thelight can be taken from the other one of the electrodes Ed and Es towhich the first voltage is not applied.

In the structure shown in FIG. 20, the placement positions of thebarrier layers B1 and B2 may be exchanged. In this case, the electricpotential at one of the electrode Ed and the electrode Es is set to behigher than the electric potential at the second electrode 22 duringdetection of light. Similarly, in the structure exemplified in FIG. 21,the placement positions of the barrier layers B1 and B2 may beexchanged. In this case, the electric potential at one of the electrodeEd and the electrode Es is set to be lower than the electric potentialat the first electrode 21 during detection of light. In thesemiconductor layer SL, carriers induced in a region sandwiched betweenthe electrode Ed and the electrode Es may be electrons or may be holes.

As described above, in the embodiments of the present disclosure,electric charges generated by photoelectric conversion are retained inthe photoelectric conversion layer and used as electric chargescontributing to the change in the permittivity of the dielectricstructure including the photoelectric conversion layer. In theembodiments of the present disclosure, movement of electric chargesbetween the photoelectric conversion layer and the electrodes issuppressed. By using the photosensor according to any of the aboveembodiments, an electric signal corresponding to the change inpermittivity due to light irradiation can be taken from the photosensor.

In the structures exemplified in the above embodiments, thephotoelectric conversion material exhibiting absorption in the infraredrange is used for the photoelectric conversion layer. The photoelectricconversion material exhibiting absorption in the infrared range has anarrow bandgap, and therefore dark current increases as the number ofthermally excited carriers increases and the value of electricalresistance decreases. Therefore, when the photoelectric conversionmaterial exhibiting absorption in the infrared range is used as thematerial of the photoelectric conversion layer, a sufficient S/N ratiomay not be obtained. However, in the embodiments of the presentdisclosure, since a barrier layer is disposed between the photoelectricconversion layer and at least one of the two electrodes, leakage to theelectrode can be reduced. In addition, the potential barrier of thebarrier layer can suppress injection of electric charges from theelectrode to the photoelectric conversion layer. For example, by readingthe change in permittivity when the potential difference between theelectrodes is changed, fixed noise due to thermal excitation etc. can beremoved. Therefore, a low-noise infrared photosensor can be obtainedusing the photoelectric conversion material exhibiting absorption in theinfrared range.

In the embodiments of the present disclosure, holes and electronsgenerated by photoelectric conversion are separated from each other byforming an electric field in the photoelectric conversion layer.Therefore, an organic compound in which the time until recombination ofholes and electrons is generally relatively short can be relativelyeasily used as the material of the photoelectric conversion layer.

As described above, according to the embodiments of the presentdisclosure, a photosensor having sensitivity in the infrared range canbe obtained using a relatively simple structure. In the photosensoraccording to any of the embodiments of the present disclosure, infraredlight is detected not through heat, and therefore it is not necessary toprovide a cooling mechanism.

The photosensor of the present disclosure is applicable tophotodetectors, image sensors, etc. By appropriately selecting thematerial of the photoelectric conversion layer, an image can be acquiredusing infrared light. The photosensor that captures an image usinginfrared light can be used for, for example, security cameras,vehicle-mounted cameras, etc. A vehicle-mounted camera can be used for,for example, input into a controller in order to allow the vehicle todrive safely. The vehicle-mounted camera can also be used to assist theoperator in order to allow the vehicle to drive safely.

What is claimed is:
 1. A photosensor comprising: a first electrode; asecond electrode; a photoelectric conversion layer between the firstelectrode and the second electrode, the photoelectric conversion layergenerating electric charges by photoelectric conversion; a first chargeblocking layer between the first electrode and the photoelectricconversion layer; a second charge blocking layer between the secondelectrode and the photoelectric conversion layer; a voltage supplycircuit configured to supply a voltage to the second electrode such thatan electric field directed from the second electrode toward the firstelectrode is generated in the photoelectric conversion layer; and atransistor having a gate connected to the first electrode, wherein: thefirst charge blocking layer is configured to suppress movement of holesfrom the photoelectric conversion layer to the first electrode andmovement of electrons from the first electrode to the photoelectricconversion layer, and the second charge blocking layer is configured tosuppress movement of electrons from the photoelectric conversion layerto the second electrode and movement of holes from the second electrodeto the photoelectric conversion layer.
 2. The photosensor according toclaim 1, wherein a voltage of the gate is changed by light incident onthe photoelectric conversion layer.
 3. The photosensor according toclaim 1, wherein the photosensor does not comprise a reset circuit forsupplying a reset voltage to the gate.
 4. The photosensor according toclaim 1, further comprising a capacitor having a first end connected tothe first electrode and a second end to which a voltage is applied. 5.The photosensor according to claim 4, wherein a capacitance valuebetween the first electrode and the second electrode without lightincident on the photoelectric conversion layer is less than acapacitance value of the capacitor.
 6. The photosensor according toclaim 1, wherein a HOMO level or a valence band level of the firstcharge blocking layer is deeper than a HOMO level or a valence bandlevel of the photoelectric conversion layer by at least 0.3 eV, and aLUMO level or a conduction band level of the first charge blocking layeris shallower than a Fermi level of the first electrode by at least 0.3eV.
 7. The photosensor according to claim 6, wherein a LUMO level or aconduction band level of the second charge blocking layer is shallowerthan a LUMO level or a conduction band level of the photoelectricconversion layer by at least 0.3 eV, and a HOMO level or a valence bandlevel of the second charge blocking layer is deeper than a Fermi levelof the second electrode by at least 0.3 eV.
 8. The photosensor accordingto claim 1, wherein at least one of the first charge blocking layer andthe second charge blocking layer includes an insulating layer.
 9. Aphotosensor comprising: a first electrode; a second electrode; aphotoelectric conversion layer between the first electrode and thesecond electrode, the photoelectric conversion layer generating electriccharges by photoelectric conversion; a first charge blocking layerbetween the first electrode and the photoelectric conversion layer; asecond charge blocking layer between the second electrode and thephotoelectric conversion layer; a voltage supply circuit configured tosupply a voltage to the second electrode such that an electric fielddirected from the first electrode toward the second electrode isgenerated in the photoelectric conversion layer; and a transistor havinga gate connected to the first electrode, wherein: the first chargeblocking layer is configured to suppress movement of electrons from thephotoelectric conversion layer to the first electrode and movement ofholes from the first electrode to the photoelectric conversion layer,and the second charge blocking layer is configured to suppress movementof holes from the photoelectric conversion layer to the second electrodeand movement of electrons from the second electrode to the photoelectricconversion layer.
 10. The photosensor according to claim 9, wherein avoltage of the gate is changed by light incident on the photoelectricconversion layer.
 11. The photosensor according to claim 9, wherein thephotosensor does not comprise a reset circuit for supplying a resetvoltage to the gate.
 12. The photosensor according to claim 9, furthercomprising a capacitor having a first end connected to the firstelectrode and a second end to which a voltage is applied.
 13. Thephotosensor according to claim 12, wherein a capacitance value betweenthe first electrode and the second electrode without light incident onthe photoelectric conversion layer is less than a capacitance value ofthe capacitor.
 14. The photosensor according to claim 9, wherein a LUMOlevel or a conduction band level of the first charge blocking layer isshallower than a LUMO level or a conduction band level of thephotoelectric conversion layer by at least 0.3 eV, and a HOMO level or avalence band level of the first charge blocking layer is deeper than aFermi level of the first electrode by at least 0.3 eV.
 15. Thephotosensor according to claim 14, wherein a HOMO level or a valenceband level of the second charge blocking layer is deeper than a HOMOlevel or a valence band level of the photoelectric conversion layer byat least 0.3 eV, and a LUMO level or a conduction band level of thesecond charge blocking layer is shallower than a Fermi level of thesecond electrode by at least 0.3 eV.
 16. The photosensor according toclaim 9, wherein at least one of the first charge blocking layer and thesecond charge blocking layer includes an insulating layer.
 17. Aphotosensor comprising: a first electrode; a second electrode; aphotoelectric conversion layer between the first electrode and thesecond electrode, the photoelectric conversion layer generating electriccharges by photoelectric conversion; a first charge blocking layerbetween the first electrode and the photoelectric conversion layer; asecond charge blocking layer between the second electrode and thephotoelectric conversion layer; a voltage supply circuit configured tosupply a voltage to the second electrode such that an electric field isgenerated in the photoelectric conversion layer; and a transistor havinga gate connected to the first electrode.
 18. The photosensor accordingto claim 17, wherein a voltage of the gate is changed by light incidenton the photoelectric conversion layer.
 19. The photosensor according toclaim 17, wherein the photosensor does not comprise a reset circuit forsupplying a reset voltage to the gate.
 20. The photosensor according toclaim 17, further comprising a capacitor having a first end connected tothe first electrode and a second end to which a voltage is applied. 21.The photosensor according to claim 20, wherein a capacitance valuebetween the first electrode and the second electrode without lightincident on the photoelectric conversion layer is less than acapacitance value of the capacitor.